464 Smith.—Cytological Studies in the Protococcales. IIP 
Literature cited. 
1 . Lagerheim, G.: Studien iiber arktische Kryptogamen. I. Uber Entwickelung von Tetra - 
edron , Ktz., nnd Enastropsis , Lag., eine neue Gattung der Hydrodictyaceen. Tromso 
Museums Aarshefter, vol. xvii, 1894, pp. [-24. 
2. Smith, G. M. : The Organization of the Colony in certain Four-celled Coenobic Algae. 
Trans. Wis. Acad. Sci., Arts, and Lett., vol. xvii, 1914, pp. 1165-1220. 
3 . --: Tetradesmus , a new Four-celled Coenobic Alga. Bull. Torr. Bot. Club, 
vol. xl, 1913, pp. 75-87. 
4 . -: The Cell Structure and Colony Formation in Scenedesmus. Arch, f. Pro- 
tistenkunde, vol. xxxii, 1914, pp. 278-97. 
5 . - : Cytological Studies in the Protococcales. I. Zoospore Formation in Chara- 
cium Sieboldii , A. Br. Ann. of Bot., vol. xxx, 1916, pp. 459-66. 
6. -: Cytological Studies in the Protococcales. II. Cell Structure and Zoospore 
Formation in Pediastrum Boryanum (Turp.), Menegh. Ann. of Bot., vol. xxx, 1916, 
pp. 467 - 79 - 
7 . West, G. S.: A Treatise on the British Freshwater Algae. Cambridge, 1904. 
EXPLANATION OF PLATE XV. 
Illustrating Professor Smith’s paper on Cell Structure and Autospore Formation in 
Tetraedron minimum. 
All the figures were drawn with the aid of the Abbe camera lucida, the drawings being made at 
the level of the base of the microscope, and with the Leitz oil-immersion objective 1/16 and ocular 4 
The magnification is about 2,100 diameters. 
Fig. 1. A young cell showing the nucleus with the pyrenoid in close association. 
Fig. 2. A slightly older cell. 
Figs. 3-5. Cells with irregular pyrenoids. 
Fig. 6. A transverse section of a cell. 
Fig. 7. A cell showing the chloroplast. 
Fig. 8. A prophase of the first nuclear division showing the ‘granules’ in the nucleus. 
Fig. 9. The spireme of the first division. 
Fig. 10. Metaphase of the first division. 
Fig. 11. Binucleate cells. 
Fig. 12. Anaphase of the second nuclear division. 
Fig. 13. A cell showing pyrenoid starch and ‘ stroma ’ starch. 
Figs. 14, 15. Four-nucleate cells. 
Fig. 16. Telophases in the third series of nuclear divisions. 
Fig. 17. Eight-nucleate cell. 
Fig. 18. An abnormal cell with more than one pyrenoid. 
Fig. 19. Completion of first cytoplasmic cleavage in the formation of four autospores. 
Fig. 20. Anaphases of nuclear division following the first cleavage. 
Fig. 21. Completion of first cytoplasmic cleavage in the formation of eight autospores. 
Figs. 22, 23. Beginning of second cytoplasmic cleavage. 
Fig. 24. Division of nuclei following the first cleavage. 
Figs. 25-8. Completion of the second cytoplasmic cleavage. 
Fig. 29. The cleavage of the cell into uninucleate protoplasts. 
Fig. 30. A later stage in the same, showing young pyrenoids. 
Fig. 31. First cleavage in the formation of sixteen autospores. 
Figs. 32, 33. The nuclear divisions following the first cleavage. 
Figs. 34, 35. Completion of cleavage into sixteen protoplasts. 
Fig. 36. Young autospores ready for liberation. 
